This invention relates to a device for controlling contents of tobacco on a cigarette manufacturing machine, and more particularly to a tobacco content control device which is capable of controlling tobacco contents constantly to a predetermined amount to guarantee production of cigarettes with uniform tobacco contents.
Reduction of production costs is a matter of utmost importance to manufacturers of cigarettes for increasing profits, and various efforts have been made to reduce such production costs.
One way of reducing production costs is to enhance the productivity of a cigarette machine. In this regard the technical developments have almost reached a stage where a single cigarette machine can produce as many as 8000 cigarettes per minute.
Another way of reducing production costs is to reduce the irregularities in tobacco contents of the individual cigarettes to be produced. Thus, in view of recent increases in leaf tobacco cost, vast profits can be made by slightly reducing the tobacco contents of the cigarettes. However unduly large reductions of the tobacco contents make it difficult to retain required quality. Accordingly, the approach generally taken in the production of cigarettes has been to measure the irregularities in weight of tobacco contents of cigarettes to check for deviations from a standard weight, and determining a target value by adding a proportional amount of tobacco to a minimum weight of tobacco which is acceptable to achieve the desired quality.
In other words, reduction of irregularities in the weight of the tobacco contents leads to minimization of the target value. This is why the cigarette manufacturers have been making great efforts to reduce irregularities in the weight of the tobacco contents of cigarettes.
In order to reduce irregularities in tobacco contents, it is important to keep a cigarette machine in good maintenance to preclude movements of worn-out mechanical parts. However, the best measure is to add a tobacco content control device of high quality to the cigarette manufacturing machine, and various devices have been proposed in this connection.
For example, Japanese Patent Appln. Pub. No. 38-18750 discloses a method of controlling the tobacco content on the basis of air permeability, utilizing correlation between the weight of a tobacco content and its air permeability. However, this method is influenced by variations in the suction pressure and the particle size composition of tobacco, which tend to disturb the pre-established correlation between the weight and air permeability of the tobacco content thereby, failing to reduce the irregularities in tobacco content to any significant degree.
U.S. Pat. Nos. 2,937,280 and 2,861,683 disclose electrostatic capacity methods based on correlation between a tobacco content and its electrostatic capacity. These methods are, however, susceptible to influences of moisture contents in the tobacco and temperature which bias the correlation between the tobacco content and electrostatic capacity. Accordingly, they hardly contribute to the reduction of irregularities in tobacco contents to any substantial degree, and have almost no practical application.
Another method for reducing irregularities in the weight of tobacco contents utilizes the correlation between a radiant ray, especially beta ray emitted from strontium 90, and the density of tobacco, controlling the tobacco contents on the basis of the transmission factor of the radiant ray. Since there is extremely reliable correlation between the transmissibility of a radiant ray and tobacco content, this method is employed by most of current cigarette manufacturing machines, in spite of such problems as safety in handling the radiant rays, and drifts and inferior response of an amplifier in a subsequent stage due to weakness of the output current of an ionization box which serves as a detection means.
The conventional tobacco content control device using a radiometric detector has a major defect, namely that, in case of a problem in a component part of the radiation detector, the measured value of transmissibility of a radiant ray which represents the tobacco content is varied irrespective of the actual tobacco content, and variations result in the tobacco contents of cigarettes to be produced. Although a radiometric detector must be handled more carefully than ordinary instruments, problem unavoidably occur with its component parts, including, for example, breakage of a foil of a metal such as titanium which is adhered to a portion where a cigarette is irradiated by an incident radiant ray, leakage of gas from an ionization box which converts the intensity of transmitted radiation into a variation in electric current, and drifts of an amplifier which amplifies the weak current output of the ionization box. These problem can take place either suddenly or gradually, so that it is necessary to check from time to time the average weight of the cigarettes being produced, i.e., the target value of the control. Normally, a suitable sample of cigarettes is weighed every ten minutes or so to guarantee a certain average weight. However, these operations are wasteful for a cigarette manufacturer and lower the labor productivity and which raises the production costs of the cigarettes.